A technique of controlling a cooling water temperature of an internal combustion engine is described in, for example, Patent Document 1. The one includes a radiator flow path in which cooling water circulates through a radiator, a bypass flow path in which cooling water circulates to bypass the radiator, and a flow rate control valve regulating cooling-water flow rates in the radiator flow path and the bypass flow path, and controls a cooling water temperature by controlling the flow rate control valve.